There have been various research efforts to develop potentially reliable and commercially viable microcellular/nanocellular foams and foaming processes. A sizeable portion of these efforts has primarily focused on foaming polymer disks or films in batch foaming processes. Using these processes, various observations have been made. In general, for many systems that produce microcellular foam, the foam morphology contains three main regions. First, at the skin, a solid polymer matrix is formed, the morphology of which is believed to be attributable to the rapid diffusion of carbon dioxide in the polymer. A conventional skin typically ranges in size from about 50 to 100 μm. The inside core of the material is typically found to contain the most uniform cell structure with cell sizes typically ranging from about 1 to 10 μm. A mix of cells with a relatively large size distribution and unfoamed polymer is typically present in a transition between the inner core of polymeric material and outer skin.
There is a need in the art to produce polymeric foamed materials that have reduced outer layer unfoamed region sizes, particularly with respect to the foamed inner core. Additionally, there is a need in the art to produce foams with decreased cell size.